It is now widely recognized and accepted that release into the atmosphere of chlorofluorocarbon(CFC)-based refrigerants, such as refrigerant R12, has a deleterious effect upon the ozone layer that surrounds the earth. Production of CFC-based refrigerants may be severely curtailed in the future, and the cost of refrigerant for service purposes is already increasing. It is therefore becoming standard practice in the refrigerant system service industry to recover, purify and reuse refrigerant in a refrigeration system under service, rather than merely to vent such refrigerant into the atmosphere and replace with new refrigerant, as had been common practice in the past U.S. Pat. Nos. 4,768,347, 4,805,416 and 4,878,356, all assigned to the assignee hereof, disclose equipment for recovering, purifying and/or recharging refrigerant in a refrigeration system service environment.
As currently envisioned, R12 refrigerant will eventually be replaced by different types of refrigerants in production of new refrigeration systems. For example, R12 refrigerant may be replaced by R134a refrigerant in the automotive industry--i.e., in automotive air conditioning systems. However, because these refrigerants and their associated lubricants-are chemically incompatible with each other, inadvertent mixture of even small amounts of the different refrigerants can cause severe damage and early failure of the refrigeration system. It has been proposed to provide different service fittings on refrigeration equipment using different types of refrigerants, but the use of adaptors and the like in the service industry may still result in inadvertent mixing of refrigerant/lubricant types, with consequent damage to the system under service or to the service equipment itself.
A further complication arises with the use of intermediate refrigerants as substitutes for R12 refrigerant, such as ternary blends made by DuPont. With severe curtailment of R12 production that may take place, it is anticipated that a significant number of refrigeration systems currently employing R12 refrigerant may eventually be retrofitted with an intermediate substitute refrigerant. Inadvertent mixing of refrigerants is considered to be an irreversible process, leading to disposal of the mixed refrigerant as hazardous waste. U.S. Pat. No. 4,939,905, assigned to the assignee hereof, discloses a refrigerant recovery system that includes a recovery compressor, a multiple-section condenser, and means for automatically distinguishing between R12, R22 and R502 refrigerants at the compressor inlet, as a function of refrigerant vapor pressure and temperature, and switching the compressor outlet among the condenser sections to prevent mixing of refrigerants in the condenser. However, the temperature/saturation pressure characteristics of R12, R134a and blend refrigerants are such that these refrigerants cannot as readily be distinguished as a function of these characteristics.
There are currently available or will soon become available at least twenty-one different refrigerants that can be employed in various types of automotive and non-automotive refrigeration equipment. There is therefore a need in the refrigeration system service industry for a device that can be employed to test refrigerant in a storage container before using the refrigerant, or in a refrigeration system before performing service on the system, that is not restricted to any particular type of refrigerant or to automotive service applications, that is particularly well adapted to identify and distinguish between and among refrigerants of different types, that is inexpensive to manufacture and market, that is readily portable, that is rapid and efficient in operation, and/or that can be employed by relatively untrained service personnel.
U.S. Pat. No. 5,158,747 discloses such a device for identifying and distinguishing between and among different types of refrigerants. The device includes a fixed volume for containing a sample of refrigerant. The refrigerant to be tested is selectively admitted into the volume in vapor phase, vapor pressure of refrigerant within the fixed volume is measured, and admission of refrigerant into the fixed volume is terminated when the vapor pressure of refrigerant contained therein reaches a preselected level. A sensor and associated electronics are coupled to the sample-containing volume for determining type of refrigerant vapor as a function of one or more selected properties of the refrigerant, and indicating such refrigerant type to an operator.
U.S. application Ser. No. 08/047,263, filed Apr. 12, 1993 and assigned to the assignee hereof, discloses an improvement on the apparatus described in the patent noted immediately above in which a fixed volume contains a refrigerant sample at controlled pressure. A thermistor provides a first electrical signal as a function of the combined effect of thermoconductivity and temperature of the refrigerant sample in the sample-containing volume, and a temperature sensor provides a second electrical signal as a function of temperature of the refrigerant vapor in the sample-containing volume essentially independent of thermoconductivity thereof. Associated electronics determine type of refrigerant in the sample-containing volume as a function of the first and second electrical signals, and thus as a function of thermoconductivity of the refrigerant sample independent of sample temperature. Since thermoconductivity of refrigerants at a given temperature and pressure varies for different refrigerant types, refrigerant type can be determined and displayed to an operator.
A general object of the present invention is to provide a method and apparatus for identifying and distinguishing a wide variety of different refrigerant types that is economical to assemble, easy to use, and reliable over an extended useful life.